The evolution of the mobile communication market brings demands for both larger system capacity and higher data rates. To boost the support for packet switched services the 3GPP has standardized so called High Speed Downlink Packet Access or HSDPA. HSDPA includes a number of features whose combination improves the network capacity, and increases the peak data rates or throughput for downlink packet traffic. The HSDPA concept relies on a transport channel, the High Speed Downlink Shared Channel (HS-DSCH), where a large amount of power and code resources are assigned to a single user at a certain Transmission Time Interval (TTI) in a time and/or code multiplex manner. Also, HSDPA uses Adaptive Modulation and Coding, fast Physical Layer Hybrid ARQ and fast packet scheduling. These features are tightly coupled and permit a per-TTI adaptation of the transmission parameters to the instantaneous variations of the radio channel quality.
According to the 3GPP standard for HSDPA [1], a user equipment (UE) shall report the perceived channel quality to UMTS Terrestrial Radio Access Network (UTRAN). This is reported by means of a Channel Quality Indicator (CQI) information element contained in the associated uplink signaling channel (HS-DPCCH). This is schematically illustrated in FIG. 1. The CQI value reported to the UE reflects the UE's capabilities to decode the user data sent on the HS-DSCH and is used by UTRAN for UE scheduling and transport block (TB) selection. The CQI-value specifies the transport block size, number of codes and a modulation from a set of reference ones that the UE is capable of supporting with a predetermined detection error. The standard mandates that the UE CQI report should target a Hybrid Automatic Repeat Request (HARQ) Block Error Rate (BLER) of 10%.
The 3GPP specification TS 25.306 [2] specifies the capabilities for HSDPA capable UE. All UE classes have a maximum TB size capability per HARQ Transmission Time Interval (TTI) specified. This means that the absolute data rate will be limited for the UE by the TTI interval and the maximum allowed TB block size. If the TB selection in UTRAN adheres to the target value of 10% BLER even for the highest TB selection, this will result in a peak throughput approximately 10% lower than the maximum theoretically possible. This is illustrated in FIG. 2.
There is a need for improved peak data rates without introducing unnecessary interference.